It is known practice to use an abradable material, also referred to as a friable material, to create dynamic sealing in a turbomachine, particularly in an aeroplane turbojet engine compressor. Such a material forms the internal surface of an external casing that it lines, and disintegrates in the event of contact with rotor blade tips. This abradable material is designed to limit the wearing of the tips of the blades despite their rotational speed, which rotational speed may exceed 8000 rpm. Furthermore, the relative speed of a rotor blade tip with respect to its seal approaches the speed of sound.
It is thus possible to design a compressor while at the same time reducing the mechanical clearance between the rotor blade tips and the internal surface of the casing. Optimization may also account for expansion, centrifugal force and certain random operating variables such as ingestion and hunting phenomena. An abradable material that forms a casing coating generally comprises aluminium, silica, polyester. The method for producing the seal makes it possible to optimize the way in which the seal behaves and performs. Application to an internal shroud collaborating with wipers is also within the bounds of possibility.
It should be noted that the expression “abradable” is often used to denote a friable material capable of producing a certain degree of sealing against a surface that is able to move with respect to this material. This material may have various compositions, structures and forms. By way of example, an axial turbomachine compressor external shroud, provided with a layer of this material, is able to create a rotary seal against the tips of the rotor blades of the said compressor. That makes it possible to maintain the integrity of the entire assembly and do so despite the deformations, even small, inherent in the turbomachine, notably deformations whereby the blades or their support lengthen as a result of centrifugal forces. By reducing the clearance between the moving blades and the casing of the fluid stream as far as possible, the effectiveness and efficiency of the turbojet engine are thus increased.
Document FR 2 993 577 A1 discloses a method for producing a corrosion-resistant abradable coating. The coating forms a wearing portion bonded to the structure of a turbomachine. The coating comprises a polyester-based matrix and an aluminium alloy filler. The coating is produced in sheets by hot-moulding. However, the strength of the sheets in question remains limited.